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Another Vibe Thread...

Could be t case output shaft bent, or bad driveline angles then if the shaft is good ? your pics are dark and hard to see, but it looks like your rear pinion angle is pointed sort of high above the DS to level with it? if so, you need to get the pinion back down to 1-3* below the DS angle to account for axle wrap. You said your leaves are stiff, but they may not be as still as you think if you are getting axle wrap. if the 6* pointed you this high up, then a 3-4* should get you in a good spot. the 8* would be way too high. since the shaft itself doesnt vibe, its either the angles, back half of the tcase, or something in the rear end. where the splines more engaged or less engaged up front? perhaps more spline engagement helped if some of the splines are worn down in the slip. Just another idea to check for . when the DS is off you can check for play
 
98stocker said:
Have you measured the yoke to be sure it is not worn out? I don't remember the exact numbers, but I think my old 8.25 yoke was about 11 thousandths wider than the ujoint. The new yoke gave the joint a nice tight fit.
Click to expand...

I was going to suggest the same thing. I fought awful vibes on my XJ for a year after lifting it 4.5" and swapping in an 8.25. I installed a SYE, tried 4 and 6 degree shims, tried 3 different driveshafts including one I had completely rebuilt and balanced by a reputable shop. I installed a different used t-case thinking my output shaft was bent or the bearing was bad. I spent probably $500 and more weekends than I care to recount trying to fix the vibes. Changing the pinion angle would change the speed at which the vibes would occur, but the only time they went away completely was when I pulled the rear shaft and drove it on the front shaft only.

As it turns out the rear pinion yoke on the axle I swapped in was either worn or defective and was maybe 1 mm wider than the u-joint. Apparently this was causing the u-joint to shift side to side at speed, which basically resulted in the axle end of the driveshaft 'wobbling' as it rotated, if you can visualize that... which in turn caused a horrible vibration.

I haven't had a chance to replace the pinion yoke and fix the issue permanently yet, but I managed to fix it temporarily, by putting a penny inside one of my u-joint caps to act as a shim of all things. Amazingly this completely cured the vibration and the Jeep is as smooth as butter up to 75 mph. I'll probably have to replace that u-joint prematurely but I've been driving it around for 5 months now with the penny in there and it's still working.

So, you might want to check your pinion yoke! Loosen your yoke straps and see if you can push your u-joint caps in slightly. If the yoke is good you should not be able to budge them. If there is any excess room in there at all, even the slightest amount, that may be the source of your vibes. You can measure them with a caliper as well.

I've seen other threads where people can't solve their driveshaft vibes no matter what they try, and after going though it myself, I have to wonder if a bad yoke was the reason...
 
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I have a 8* shim in the rear currently. The rear pinion angle and the driveshaft are *exactly* the same angle. I'll probably go back to a 6* shim as most have recommended.

I don't believe it is the back half of the transfer case as there is no play in the output shaft, it spins on center and it was perfect prior to regearing.

I'm running the OEM front shaft right now. The splines were less engaged when used in the rear than they are now (back in the front).

When more weight is added to the rearend, what will happen to the pinion angle? The reason I'm asking is I do not have my skid plate (aftermarket), hitch, bumper (oem), spare tire carrier (detours tailbone) or spare tire on it right now. That is several hundred pounds that I will be adding.
 
Id throw the 6* in there to start, as well the rear pinion yoke idea. If the yoke allows play in the u joint that will cause vibes. A new yoke and pinion nut would probably run you around 60$ shipped.
 
I'm game for anything @ this point. I'll definitely go back to 6* shims and will go ahead and buy a new pinion and nut. The guy who did my install is going to take a look inside the rear diff next weekend. I'll see about having him install the new yoke then.

I *really* appreciate all of the help with this. I've spent about 5-6k rebuilding this entire vehicle over the past year & am pretty down that I can't drive over 45mph in it! ;-) My reason for keeping it low was so it drove awesome & had no vibes! Not to mention, it is a hunting/trail vehicle mainly. No crawling.
 
id have that guy inspect it before you buy a yoke and nut in case that ends up not being the problem. you should be able to inspect the yoke with the rear DS on and look for side to side slop.
 
Here is what that tells me, the issue is most likely driveline related and not the axle. The vibration was present both under acceleration and coast with a rear drive shaft installed. You removed the driveshaft and now have absolutely no vibration. The ring and pinion are still spinning, albeit with out a load on them. If there was a vibration being caused by them or with an issue in the bearings it should still be present, even if reduced. That leads me to believe its something else causing it.

I realize the vibes weren't there prior to the gear install but as previously stated the driveshaft is having to spin a lot faster now at 50mph then it did before.

Check the yoke for wear, if you do find it needs replacing I'd look for one that upgrades you to U-bolts on the u-joint instead of straps. If you're buying one anyways you might as well upgrade.

I'd still plan to have the cover popped off and check out the ring, pinion, and bearings too just to make sure. Pop the carrier out too and re-verify pinion bearing pre-load.
 
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Moved back to 6* shims this weekend (about 2* down now) and then adjusted the front axle. Running 4* caster now with my front pinion about 1.75* down. Running with the front driveshaft only, awesome. No odd noises/vibes/etc.

Last night, I decided to measure the rear yoke for wear (none) and grease up/re-install the TW rear driveshaft. Fits perfect, no play in any direction. I also checked the yoke for "notchy" turning, smooth as can be. I think I was hoping for devine intervention or something. The rear vibes are still there, just as bad as ever.

The driveshafts (both the oem front and the TW rear) are both balanced as I have now run them both up front and they are smooth as glass up to 70mph. Hopefully going to get the rear axle looked @ this weekend. If we're unable to find anything wrong w/ the rear diff, I may pick up another 8.25 to throw it under - just for a test. I'm at a loss.
 
Good call on the other axle. Have you checked the tcase rear output shaft + bearings for wear?

have you popped the rear diff cover to see if anything weird has happened?
 
Over the weekend, I pulled the rear "cone" off of the transfer case to check the seal/bearing and look for wear on the shaft. Nothing. Sealed it back up and everything spins smoothly, no noise, and the shaft is tight (no play in any direction).

I haven't popped the diff cover myself. Mainly b/c the guy who regeared it has offered to take a look this coming weekend.

Took it out last night just to verify a few things (both shafts attached). The vibration is there in 2wd/4wd - above 45mph it gets bad. I took it up to 65, no signs of stopping (it gets worse). If I let off the gas, no change. Shift the trans into neutral @ 65, still there.

I'll keep reporting back. Hopefully we discover something this weekend. If not, going to pickup the 2nd 8.25 for testing.
 
notamos said:
Over the weekend, I pulled the rear "cone" off of the transfer case to check the seal/bearing and look for wear on the shaft. Nothing. Sealed it back up and everything spins smoothly, no noise, and the shaft is tight (no play in any direction).
Click to expand...

Ignore this if you did check already, but did you look for runout? Things may be tight but if the transfer case mainshaft or the rear pinion (much less likely...) are bent, it will vibrate badly. Just check with both shafts disconnected from the t-case, put a drill+socket attachment on the front output shaft nut and in 4wd look at the rear output see if it wobbles?

If that checks, maybe do similar for the rear pinion?

Cheers
 
Well, I *think* I know what your asking. What I did - disconnect both driveshafts, put the transfer case in 4hi and then shift the transmission into drive. Both yokes on the tcase were spinning - no visible vibration/spinning off-center. I did *not* take the RPMs above idle, so I do need to try that. Also, I need to jack up the rear end (loaded) and put it in gear to see if the rear yoke spins properly (visibly) when "driving".
 
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This is when one of those go-pro HD cameras would be great, strapped under the truck, aimed at the driveshaft. Or a Darwin award candidate buddy :)

Maybe just a laptop on the passenger seat and some cheap webcam on a long cable with an extension cable? This way the webcam gets ripped out it's not so bad and doesn't pull the laptop with it...
 
I'll do it & it there is nothing visible in the garage, I'll hook up a USB cam and go driving. Oddly enough, I had already thought about the "darwin award candidate buddy" and a skateboard... ;-)
 
With a camera down there, and the vibes start..... The cam will just start shaking as well. Been there.
I just put the jeep up on stands, in the street with a strap to another truck from the jeeps rear bumper. Keep it tight.
Make sure all is clear if it were to drop. Use mirrors to see where you need to see when the drive line starts shakin.
Obviously don't get in front, or under it while spinning it up. duh.
Easy button - Ding.
 
Haven't had the chance to get together w/ my gear dude yet. Weather and all.

WHY would extremely cold weather (like under 10deg) make this vibration better, from a cold start? Yesterday morning I took it out and the vibrations were almost gone from 40-55. Eventually they started to come back, although slowly. I'm thinking while the gear oil in the rear diff was thick?

-NA
 
Gear dude checked out the rear diff, said there were no issues w/ it @ all. He said he thought there were angle issues w/ the pinion/driveshaft - there isn't. I measured it multiple times w/ two different angle finders & the driveshaft/pinion angle are exactly the same. I *could* lower the pinion 2deg down but, honestly, don't think it will do shit. I was going to take the driveshaft down to Boulder yesterday to have it rebalanced but the guy @ the shop talked to me at length about the problems & thinks I'm wasting my time looking @ the driveshaft as the culprit.

This morning - cold again. The vibes were better until it warmed up the fluids...
 
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